A cyclic olefin-based copolymer of a first invention of the present application has a constitutional unit (A) derived from an α-olef in having 2 to 20 carbon atoms, a constitutional unit (B) derived from a cyclic olefin without an aromatic ring, and a constitutional unit (C) derived from a cyclic olefin having an aromatic ring.A medical container of a second invention of the present application contains a cyclic olefin-based copolymer having a constitutional unit (A) derived from an α-olefin having 2 to 20 carbon atoms, a constitutional unit (B) derived from a cyclic olefin without an aromatic ring, and a constitutional unit (C) derived from a cyclic olefin having an aromatic ring.